1. Field of the Invention
This invention relates to a ball bearing for an electromagnetic clutch and pulley and for a driveshaft of a compressor for an automobile air conditioner. The bearing comprises an inner ring secured to a fixed shaft of the compressor, an outer ring integrally and rotatably secured to the pulley of the compressor, and balls therebetween, wherein the bearing is adapted to bear a radial load by the pulley, an axial load by the electromagnetic clutch disposed adjacent the pulley and a rotational moment load owing to an offset between the centers of load of the bearing and the pulley in an axial direction.
2. Description of the Related Art
A prior art double-row ball bearing for an electromagnetic clutch and pulley and for a driveshaft of a compressor for an automobile air conditioner is shown, for example, in FIG. 8. The double-row ball bearing 80 has an one-piece inner ring 92 secured to a fixed shaft 86 protruded from a compressor housing 82 of the compressor 81, an one-piece outer ring 93 secured to an inner surface 87 of a pulley hub 91 integrally and rotatably formed with the pulley 88 of the compressor 81, and double-row balls therebetween. An electromagnetic coil windings 94 is secured to the compressor housing 82 and enclosed within the pulley hub 91. The pulley hub 91 includes a radial portion having a friction clutch surface 90 situated directly adjacent a friction clutch engagement plate 85 having an armature 89 thereon. A compressor driveshaft 83 is connected drivably to the engagement plate 85 on its free end. When the electromagnetic coil windings 94 is energized, the armature 89 is attracted toward the coil windings 94 and the clutch engagement plate 85 is engaged with the friction clutch surface 90, thus the electromagnetic clutch is engaged, and a rotational driving force by the pulley 88 is transmitted to the driveshaft 83 through the armature 89 and the engagement plate 85. The driveshaft 83 rotates a rotor fixed to it and the compressor is operated.
By such an arrangement, the bearing 80 is adapted to bear a radial load by the pulley 88 loaded by belts not shown, an axial magnetic load by an electromagnetic clutch coil windings 94 when the coil windings 94 is energized. Usually, due to limited spaces for automobile engine auxiliary parts not shown, the centers of load of the bearing 80 and the pulley 88 are offset or discrepant in an axial direction. Such offsetting of the centers of load acts a rotational moment load againist the plane perpendicular to the axis of the bearing 80 to rotate the bearing 80 in an axial direction. This rotational moment load results a relative inclination between the axes of inner and outer rings 92, 93. Further, when this relative inclination become greater, an air gap G in an axial direction between the friction clutch surface 90 and the armature 89 is also enlarged, thereby results that an attractive force by the coil windings 94 is weakened. This further leads to fail an engagement between the friction clutch surface 90 and the armature 89, or due to the weakened attractive force a relative slippage therebetween occurs, causing the rotational driving force by the pulley 88 is not transmitted to the driveshaft 83, or causes to generate a heat between the friction clutch surface 90 and the armature 89. On the other hand, when this air gap G is smaller, portions of the friction clutch surface 90 and the armature 89 are made always to contact causing a generation of heat or malfunctions.
It is required that a relative inclination between the axes of inner and outer rings of a compressor bearing must be less than 0.3 degree, when the bearing is loaded with a radial load by a pulley, an axial magnetic load by an electromagnetic clutch and a rotational moment load at the same time, further, number of revolution of the bearing is required to be high revolutions of about 10,000 rpm.
By these reasons, as a ball bearing for an electromagnetic clutch and pulley and for a driveshaft of a compressor for an air conditioner, conventionally, the double-row ball bearing 80 as shown in FIG. 8, or a pair of single-row deep-groove ball bearings as shown in U.S. Pat. No. 5,275,269 is used to keep a relative inclination between the axes of inner and outer rings small when the bearing is loaded with the radial, axial and rotational moment loads at the same time. However, since the double-row ball bearing 80 or a pair of single-row deep-groove ball bearings is expensive and requires much space in an axial direction.
The inventors of this invention know that a single-row three-point-contact ball bearing as disclosed in G.B.patent No.1257658 or a single-row multi-point-contact ball bearing including a four-point-contact ball bearing is less expensive and requires a less space in an axial direction during to the relative displacement between its both rings is small when such bearing is loaded with the above radial, axial and rotational loads at the same time. However, the inventors do not know that any one of these bearings is used for a bearing for a compressor for an air conditioner which is affected by the above radial, axial and rotational loads at the same time under a required high revolutions of about 10,000 rpm.